Electric drive system

ABSTRACT

The invention relates to an electric drive system, comprising an n-phase electric machine, n&gt;1, which has at least two single-phase winding strands, a first inverter, the output connection of which is connected to the phase connection of a first of the single-phase winding strands of the electric machine, at least one second inverter, the output connection of which is connected to the phase connection of a second of the single-phase winding strands of the electric machine, and a DC voltage source which has a plurality of series-connected battery modules and the output connections of which are respectively connected to the input connections of the first inverter and to the input connections of the second inverter, so that the first inverter and the second inverter are arranged in parallel.

BACKGROUND OF THE INVENTION

The invention relates to an electric drive system, in particular for anelectrically operated vehicle such as an electric car or a hybridvehicle.

As is depicted in FIG. 1 by way of example, the feed of an electricmachine 101 takes place in an electric drive system 100 typically bymeans of an inverter 102 in the form of a pulse width modulatedinverter. To this end, a DC voltage provided by a DC voltageintermediate circuit 103 can be converted into a multi-phase AC voltage,for example a three-phase AC voltage. The DC voltage intermediatecircuit 103 is fed by a string consisting of series-connected batterymodules 105 or any desired DC voltage sources.

In order to be able to meet the requirements for power and energy givenfor a respective application, a plurality of battery modules or batterycells are frequently connected in series in an energy storage system. Ifhowever high power outputs are required from the electric machine, itmay be necessary to take measures in implementing the electric drivesystem 100 that meet the increased power output requirements.

It can, for example, be possible to connect a plurality of strings 104consisting of series-connected battery modules 105 in parallel. This canhowever lead to undesired compensation currents between the strings 104.In addition, it may also be necessary to increase the current carryingcapacity of the inverter 102 and the electric machine 101.Alternatively, the intermediate circuit voltage could also be raised. Inany case, extensive adaptations and changes in the implementation of theelectric drive system will be necessary, which in turn lead to increasedimplementation effort and costs.

The American patent publication US 2007/0070667 discloses a drive systemfor an electrically operated vehicle comprising multiple invertersconnected in parallel, which supply AC voltage to a multi-phase motor.The German patent publication DE 10 2011 085 731 A1 discloses anelectric drive system for a six-phase motor comprising two invertersconnected in parallel. The German patent publication DE 10 2008 008 978A1 discloses modular drive converters. The German patent publication DE10 2010 001 250 A1 discloses an electric drive system for an electricmachine comprising two phase systems, which are fed via separateinverters.

SUMMARY OF THE INVENTION

According to a first aspect, the present invention relates to anelectric drive system, comprising an n-phase electric machine, n>1,which has at least two single-phase winding strands, a first inverter,the output connection of which is connected to the phase connection of afirst of the single-phase wiring strands of the electric machine, atleast one second inverter, the output connection of which is connectedto the phase connection of a second of the single-phase winding strandsof the electric machine, and a DC voltage source which has a pluralityof series-connected battery modules and the output connections of whichare respectively connected to the input connections of the firstinverter and to the input connections of the second inverter, so thatthe first inverter and the second inverter are arranged in parallel.

A concept of the present invention is to actuate electric machines withthe help of standardized power modules, such as inverters, for examplein B6 topology. Such inverters are available as standardized moduletypes which can be cost effectively procured and implemented by means ofeconomy of scale effects. The performance of the electric drive systemis advantageously increased by the modularization of the power moduleswithout the design of the electric machine or the individual powermodules being more complicated or cost intensive per se. Simplemechanical connection means, by means of which the system modules can beinterconnected, can furthermore be provided for all of the powermodules. In addition, a central control device, for example on a centralcontrol circuit board, can be similarly provided for all power modules.

According to one embodiment of the electric drive system according tothe invention, the first and the second inverter can each have asingle-phase, self-piloted inverter which comprises a symmetrical halfbridge consisting in each case of two power semiconductor switchesconnected in series.

According to a further embodiment of the electric drive system accordingto the invention, the switching elements can each comprise powersemiconductor switches, preferably MOSFET switches or IGBT switches.These switches are particularly able to withstand stress and can bereliably actuated.

According to a further embodiment of the electric drive system accordingto the invention, the drive system can furthermore comprise a controldevice which is designed to actuate the power semiconductor switches ofthe first inverter and the second inverter, wherein the control deviceis disposed on a central control circuit board for the first inverterand the second inverter.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of embodiments of the invention ensuefrom the following description with reference to the attached drawings.

In the drawings:

FIG. 1 shows a schematic depiction of an exemplary conventional electricdrive system; and

FIG. 2 shows a schematic depiction of an electric drive system accordingto a further embodiment of the present invention.

Identical reference signs generally denote similar or similarlyfunctioning components. The schematic depictions shown in the figuresare only of an exemplary nature and are depicted in an idealized mannerfor reasons of clarity. It goes without saying that the depictedcomponents are only used to illustrate principles and functional aspectsof the present invention.

DETAILED DESCRIPTION

FIG. 2 shows ultimately a schematic depiction of an electric drivesystem 40, comprising an n-phase electric machine, n>1, which, forexample, can be a switched reluctance machine or a three-phase machine.The electric machine has, by way of example, four single-phase wiringstrands 6 a to 6 d, which can be coupled to one another at the neutralpoint thereof. The electric drive system 40 furthermore has an invertersystem consisting of four inverters 7 a to 7 d coupled in parallel. Inso doing, each of the four inverters 7 a to 7 d, at the outputconnections thereof, feeds respectively one of the single-phase windingstrands 6 a to 6 d of the electric machine 6.

The inverters 7 a to 7 d each have a half-bridge topology, i.e. each ofthe inverters represents a single-phase, self-piloted inverter whichcomprises a symmetrical half bridge consisting respectively of two powersemiconductor switches H1 and H2 in a series circuit. The powersemiconductor switches can, for example, be MOSFET switches or IGBTswitches. It is, however, also thereby possible to use any other type ofswitching elements as switches H1 and H2 and at the same time to connecta free-wheeling diode in parallel to each switching element H1 and H2.The phase of the single-phase winding strands 6 a to 6 d is coupledrespectively to a center tap of the half bridge of the inverters 7 a to7 d.

The inverters 7 a to 7 d can thereby be implemented either as separateinverter units or also in a common inverter module. In the latter case,a single inverter module comprising four symmetrical half bridges can beprovided which is coupled in a suitable manner to the electric machine6. A (not explicitly depicted) control device, which, for example, canbe implemented on a common control circuit board, can be used for theactuation of the power semiconductor switches H1, H2.

The inverters 7 a to 7 d can, for example, be supplied with anelectrical DC voltage by means of a common DC voltage source 1, forexample a traction battery of an electric vehicle. To this end, the DCvoltage source 1 can, for example, comprise a series circuit consistingof battery modules 5, the number of which is depicted as 3 in FIG. 2only by way of example. Any other number of battery modules 5 canlikewise be possible. It is likewise possible to connect more than fourinverters in parallel, in particular if the electric machine 6 has morethan four winding strands 6 a to 6 d. To this end, each of the inverterscan be associated with one of the winding strands and be electricallyconnected to the same.

By using a plurality of basically similar inverters 7 a to 7 d, thephase currents can be kept the same through each of the inverters 7 a to7 d, even if the number of the inverters 7 a to 7 d is greater than one.As a result, the current carrying capacity of the power semiconductorswitches H1, H2 of the inverters 7 a to 7 d does not have to beincreased with respect to conventional power semiconductor switches. Inaddition, each of the inverters 7 a to 7 d can also be supplied from aseparate DC voltage source 1. A feed of a four-phase electric machine 6,as depicted in FIG. 2, can, for example, also take place by means of twoseparate DC voltage sources 1, which in this variant can advantageouslyin each case alternately feed adjacent inverters. That means adjacentwinding strands of the electric machine 5 are served respectively bydifferent DC voltage sources 1.

In the drive system depicted in FIG. 2, the electric machine 6 can, forexample, be a synchronous or asynchronous machine, a reluctance machineor a brushless DC motor (BLDC). It may also be possible to use theelectric drive system 40 of FIG. 2 in stationary systems, for example inpower plants, in electrical power generation plants, such as wind powerplants, photovoltaic plants or power-heat coupling plants, in energystorage plants, such as, for example, compressed air storage powerplants, battery storage power plants, flywheel accumulators, pumpedstorages or similar systems. A further option for use of the electricdrive system 40 of FIG. 2 is in passenger vessels or commercialtransport vessels which are designed to move on or under the water, forexample ships, motor boats or something similar.

1. An electric drive system (40), comprising: an n-phase electricmachine (6), n>1, which has at least two single-phase winding strands (6a, 6 b); a first inverter (7 a), the output connection of which isconnected to the phase connection of a first of the single-phase windingstrands (6 a) of the electric machine (6); at least one second inverter(7 b), the output connection of which is connected to the phaseconnection of a second of the single-phase winding strands (6 b) of theelectric machine (6); and a DC voltage source (1) which has a pluralityof series-connected battery modules (5), output connections (1) of whichare respectively connected to the input connections of the firstinverter (7 a) and to the input connections of the second inverter (7b), so that the first inverter (7 a) and the second inverter (7 b) arearranged in parallel.
 2. The electric drive system (40) according toclaim 1, wherein the first and the at least one second inverter (7 a, 7b) each represent a single-phase, self-piloted inverter, which comprisesa symmetrical half bridge including respectively two power semiconductorswitches (H1, H2) connected in series.
 3. The electric drive system (40)according to claim 2, wherein the power semiconductor switches (H1, H2)are MOSFET switches or IGBT switches.
 4. The electric drive system (40)according to claim 2, further comprising: a control device, configuredto actuate the power semiconductor switches (H1, H2) of the firstinverter (7 a) and the second inverter (7 b), wherein the control deviceis disposed on a central control circuit board for the first inverter (7a) and the second inverter (7 b).